1. Field of the Invention
This invention relates to a proteinase-resistant cellulase, a microorganism producing the same, and a process for producing such a proteinase-resistant cellulase.
2. Description of the Background
Conventionally, studies on cellulose-decomposable enzymes (cellulases) have been undertaken for the purpose of effective utilization of biomass resources. Examples of cellulases heretofore reported include those derived from molds belonging to the genera Trichoderma, Aspergillus, Acremonium, Humicola; bacteria belonging to the genera Pseudomonas, Cellulomonas, Ruminococcus, Bacillus; and ray fungi belonging to the genera Streptococcus, Actinomyces; and the like. At the present time, however, few cellulases utilizing biomass resources are produced in an industrial scale.
In the area of utilization of cellulases, on the other hand, the application of cellulases as an additive to detergents for washing clothes is lately on the increase (Japanese Patent Publication (kokoku) Nos. 49279/1984, 23158/1985, 36240/1985, etc.). Several processes are known for producing alkaline cellulases which can be used as a component of detergent compositions for washing clothes. Such processes include a process for collecting cellulase A by culturing an alkalophilic microorganism belonging to the genus Bacillus (Japanese Patent Publication (kokoku) No. 28515/1975), a process for producing alkaline cellulase 301-A by culturing an alkalophilic microorganism belonging to the genus Cellulomonas (Japanese Patent Laid-open (kokai) No. 224686/1983), a process for obtaining carboxymethyl cellulase (CMC) by culturing an alkalophilic microorganism, Bacillus sp. No. 1139 [Horikoshi et al.; J. Gen. Microbiol., 131, 3339 (1985)], a process for producing an alkaline cellulase with the use of a microorganism belonging to the genus Streptomyces (Japanese Patent Laid-open (ko-kai) No. 19483/1986), and a process for producing alkaline cellulase K by the culture of Bacillus sp. KSM-635 which is also a species of alkalophilic microorganisms (Japanese Patent Laid-open (ko-kai) No. 109776/1988). Beside these processes for producing alkaline cellulases, there are reports for the production of alkali-resistant cellulases such as alkali-resistant cellulases K-522 and K-588 (Japanese Patent Laid-open (ko-kai) Nos. 37285/1989 and 37286/1989).
All these cellulases, however, are not proteinase-resistant, and thus can not be incorporated in detergent compositions for washing clothes containing a proteinase. The means to overcome this problem such as the immobilization of a cellulase or the stabilization of a cellulase by chemical modification are not appropriate to industrial application because of the cost involved and the poor yields which can be achieved.
The development of cellulases which are inherently proteinase-resistant and are suitable for use as a component of detergent compositions for washing clothes is therefore desired.
In view of this situation, the present inventors have undertaken extensive studies in order to overcome the above problems and to obtain microorganisms capable of producing proteinase-resistant cellulases, and, as a result, discovered a cellulase which satisfies the above requirements among cellulases produced by specific microorganisms belonging to the genus Aspergillus.